1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to heat treatments necessary for processes of diffusing and activating impurities.
2. Description of Related Art
Performance improvement in recent large-scale integrated circuits (LSI) has been achieved by enhancing the degree of integration; in other words, by miniaturization of the device configuring the LSI. However, with miniaturization of the device, a parasitic resistance and a short channel effect have been prone to occur. Hence, it becomes important to form shallow and low-resistant impurity diffusion regions (source/drain regions) in order to prevent the parasitic resistance and the short channel effect.
In order to lower the resistance of the impurity diffusion regions, it is important to fully activate impurities by use of a high-temperature annealing treatment such as a rapid thermal annealing (RTA) treatment utilizing a halogen lamp.
Meanwhile, shallow formation of the impurity diffusion regions is realized by implanting impurity ions by means of low acceleration energy and by optimizing the subsequent annealing treatment. For example, in a flash lamp annealing method using a xenon (Xe) flash lamp, the xenon flash lamp emits white light for 10 msec or less, thereby instantaneously supplying the energy necessary to activate the impurities. Hence, the low-resistant and shallow impurity diffusion regions can be formed. Specifically, the flash lamp annealing method enables the impurities implanted into monocrystalline silicon to be activated without changing the distribution of the impurity ions at all. It should be noted that by use of an excimer laser capable of pulse oscillation, the low-resistant and shallow impurity diffusion regions can be similarly formed.
However, in the RTA treatment using the halogen lamp, diffusion coefficients of the impurities such as boron (B), phosphorus (P) and arsenic (As) in the monocrystalline silicon are large, and therefore, the impurities are diffused inside and outside the monocrystalline silicon, thus making it difficult to form a shallow impurity diffusion layer. When lowering the annealing temperature for the purpose of restricting the diffusion of the impurities, the activation ratio of the impurities is greatly lowered. Hence, in accordance with the RTA treatment using the halogen lamp, it is difficult to form the low-resistant and shallow impurity diffusion regions.
Meanwhile, in the flash lamp annealing method, impurity ions implanted simultaneously into a polycrystalline gate electrode when implanting the impurity ions into the impurity diffusion regions are not diffused either, rather, they suffer from the annealing time which is extremely short. Therefore, the impurity ions implanted into the polycrystalline gate electrode are not diffused entirely into the polycrystalline gate electrode, and a highly resistive region in which impurity concentration is low is formed in a part of the polycrystalline gate electrode. This resistance increase of the gate electrode lowers the driving power of the transistor. Specifically, in accordance with the flash lamp annealing method, even if the low-resistant and shallow impurity diffusion regions can be formed, it is impossible to form a high-performance micro transistor.